Method and apparatus for turbine internal visual inspection with foveated optical head and dual image display

ABSTRACT

Turbine engines are inspected by insertion of a zoom image or foveated image optical head through internal passages within the engine. The zoom image optical generates a first magnified image portion or a second image portion having a wider field of view and lower magnification. The foveated image optical head has a central first image portion having higher magnification that is included within and subtended by a second image portion having a wider field of view. The foveated or zoom image first and second image portions are separately simultaneously displayed on a common display, so that navigation position of the optical head and the magnified inspection image are correlated. In this way an inspector can confirm what area of interest within the turbine has been inspected while evaluating the adjacent magnified inspection image. The dual images correlation can be documented, such as by storing the simultaneously displayed images.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application incorporates by reference in its entirety United Statesutility patent application entitled “METHOD AND APPARATUS FOR TURBINEINTERNAL VISUAL INSPECTION WITH FOVEATED IMAGE OPTICAL HEAD”, filedconcurrently herewith and assigned Ser. No. 14/601,266.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to internal visual inspection of turbine engines,such as combustion/gas turbine engines or steam turbine engines byinsertion of optical cameras through internal passages within the enginevia a delivery mechanism, such as an elongated articulated arm orflexible conduit. More particularly the invention relates to borescopeshaving zoom or foveated image optical heads. Foveated image opticalheads generate an optical image with a central first image portionhaving higher magnification and smaller field of view that is includedwithin and subtended by a second image portion having a wider field ofview and lower magnification. The first and second portions of the zoomor foveated image are simultaneously displayed on a common visualdisplay so that an inspector can identify optical head position withinthe engine during its navigation while inspecting the magnified image.

2. Description of the Prior Art

Steam or combustion turbine engines in electric power generation plantsrequire periodic scheduled inspection and maintenance. Gas or combustionturbine engines are more frequently subject to intermittent operation tomeet fluctuating power demands; hence for both economic and operationalefficiency it is desirable to perform periodic visual internalinspections of the assembled engines between power demand cycles.

A common way to perform visual inspection of blades and vanes incompressor and turbine sections of the engines is by insertion of arigid, articulate arm or flexible conduit borescope through inspectionports that are constructed about the engine periphery. Many of thoseinspection ports have inner diameters of less than 13 mm. Engineinternal passageways from the inspection ports to areas of interest havetight confines that physically limit maneuvering space for borescopeoptical heads. As a practical matter optical heads having axial lengthgreater than 40 mm cannot be maneuvered through confines of some turbineinternal passageways.

When maneuvering a borescope through turbine engine internal passages itis helpful to have a sufficiently wide angle field of view (FOV) for theinspector to be able to identify relative navigation position of theborescope optical head within the engine, so that the areas of interestcan be reached efficiently. The wide angle view also allows theinspector to confirm that the desired area of interest has beeninspected. However, the wide angle view often does not have sufficientmagnification to perform visual inspection within the area of interest.

Image field of view (FOV) and magnification are interrelated. Generally,for a given lens or lens train design, increasing the FOV decreasesmagnification. Optical head dimensional envelope constraints alsoconstrain optical performance capabilities. It is desirable to maneuvera borescope optical head within the inspected engine with a relativelywide field of view lens train, but the resultant magnification may notbe sufficient to perform a satisfactory visual inspection once theoptical head is positioned to an area of interest, for exampleinspecting for cracks or spallation of a turbine blade airfoil externalsurface thermal barrier coat. One previously known inspectionmagnification solution was to remove the lower magnification borescopeand replace it with a higher magnification, smaller FOV borescope whereneeded for more detailed inspection. Another previously known solutionfor turbine engine internal inspection has been use of a variableFOV/magnification borescopes, but many have optical heads that are toolarge to fit within the small dimensional confines of desired inspectionports. For example, borescopes have been constructed with separate,dedicated completely separate parallel optical paths or beam splittingdownstream of the primary objective lens for different FOV/magnificationrequirements: essentially two separate optical instruments in a sharedoptical head. Generally the parallel optical path optical heads haveeither larger diameter or axial length than allowable for insertion intomany turbine engine inspection ports. Other borescopes have zoommagnification capability by physically varying axial spacing betweenlenses in the lens train and/or the image detector at the design cost ofoptical head added axial length. Yet other borescopes rely electronicimage processing to substitute for physical lens FOV/magnificationadjustment. The electronic image processing can include: (i) separatededicated sections of a common electronic detector for eachFOV/magnification setting or (ii) post image gathering enlarged pixeldisplay. Either of those electronic imaging processing techniquesdecreases image detail. In the case of (i) less than the entireavailable image sensor pixel density is used to provide image detail. Inthe case of (ii) the enlarge pixels do not contain any additional imagedetail compared to a true magnified image view. There has also beenconcern that inclusion of electronic devices, such as lens autofocusmechanisms or adjustable lens shaping mechanisms, in optical heads thatare exposed to heated ambient temperatures within cooling engines mightlead to failure of those electronic mechanisms.

When maneuvering a borescope through turbine engine internal passages itis also helpful to be able to correlate and document inspectionnavigation position within the turbine with the magnified inspectionimage

SUMMARY OF THE INVENTION

Exemplary embodiments described in greater detail herein incorporatezoom or foveated image optical heads that are inserted to combustion orsteam turbine engines internal areas of interest. The foveated imageoptical head has a central first image portion having highermagnification and smaller field of view that is included within andsubtended by a second image portion having a wider field of view andlower magnification. The foveated image first magnified image portionand second wide angle image portion are separately simultaneouslydisplayed on a common display, so that navigation position of theoptical head and the magnified inspection image are correlated. In thisway an inspector can confirm what area of interest within the turbinehas been inspected while evaluating the adjacent magnified inspectionimage. The dual images correlation can be documented, such as by storingthe simultaneously displayed images. In some exemplary embodiments thefoveated image is generated with a monolithic aspheric objective lens.In other exemplary embodiments a first liquid lens is aligned along thesame optical path as the objective lens for selectively transmitting thefoveated image first or second portions. In other exemplary embodimentsa second focusing liquid lens is aligned along the same common opticalpath as objective lens and the first liquid lens for selectivelyenhancing image focus. The foveated image optical head facilitatesmaneuvering the borescope optical head through the turbine engine withthe wider field of view second image portion to areas of interest, thenperforming a more detailed inspection by viewing the highermagnification first image portion. The optical head lenses are in fixedpositions, sharing a single, common optical path and a common electronicimage sensor. This lens and detector arrangement facilitatesconstruction of a compact optical head, which in some embodiments has anouter diameter of less than 11 mm and an axial length less than 40 mm,allowing passage through small diameter engine inspection ports.

Other exemplary embodiments described herein provide for simultaneousseparate common display of the first higher magnification and the secondwider FOV foveated image portions by switching the first liquid lenssequentially between two focusing states and displaying the image feedsin parallel on separate dedicated portions of a common shared imagingscreen, which may include a wearable imaging screen device, such aseyeglasses. Alternatively the same simultaneous separate common displayof the first higher magnification and the second wider angle imageportions common can be performed with non-foveated images.

Exemplary embodiments of the invention feature a method for dual fieldof view internal visual inspection of a turbine engine by providing aninspection system including a borescope capable of generating a foveatedimage on a single optical path, with a first central image portionhaving a first angular field of view and magnification that is includedwithin and subtended by a second image portion having a second widerangle field of view and lower magnification. The borescope is insertedinto the turbine engine from its exterior through engine internalpassages to an internal area of interest. The first image portion of theinternal area of interest within the engine is captured with theinspection system. Then the second image portion of the internal area ofinterest within the engine is captured with the inspection system. Boththe first and second separately captured image portions simultaneouslyand separately displayed on a common video display that is coupled tothe inspection system. In some embodiments the correlated first andsecond image portions are archived or otherwise stored, so that theinspection location (wide angle view) and the magnified inspection imagecan be commonly referenced in the future.

Other exemplary embodiments of the invention feature a method for dualfield of view internal visual inspection of a turbine engine byproviding an inspection system including a borescope having an elongateddelivery mechanism having a distal end for insertion from an exterior ofa turbine engine through internal passages within the engine to areas ofinterest and an optical head coupled to the delivery mechanism distalend. The optical head includes on a shared common optical path anobjective lens capable of transmitting a foveated image with a firstcentral image portion having a first angular field of view andmagnification that is that is included within and subtended by a secondouter concentric image portion having a second wider angle field of viewand lower magnification; a first liquid lens, for selectively separatelytransmitting the foveated image first or second portions that werereceived from the objective lens; and a second liquid lens forselectively enhancing focus of images received from the first liquidlens. The respective lenses coupled in fixed axial positions along ashared optical path within the optical head. Additionally an electronicimage sensor is optically coupled to the second liquid lens, for commoncapture and transmission of images received from the second liquid lens.A liquid lens control system is coupled to the first liquid lens, forselectively causing the first liquid lens to transmit separately firstor second image portions received from the objective lens, and coupledto the second liquid lens for selectively causing the second liquid lensto enhance focus of images transmitted by the first liquid lens. Animaging system is coupled to the common electronic image sensor, forselectively generating the foveated image first or second portions,viewable outside the exterior of the inspected turbine engine. Theinspection optical head is inserted into the turbine engine from itsexterior to an internal area of interest by routing the deliverymechanism through engine internal passages. The liquid lens controlsystem causes the first liquid lens to transmit sequentially separatefirst and second image portions of the internal area of interest withinthe engine. The captured first and second image portions are transmittedby the first liquid lens to the electronic image sensor, for furtherprocessing by the imaging system. Both the first and second separatelycaptured image portions are displayed on a common video display that iscoupled to the imaging system.

Additional exemplary embodiments of the invention feature a turbineengine dual field of view internal inspection system, which includes aborescope having an elongated delivery mechanism having a distal end forinsertion from an exterior of a turbine engine through internal passageswithin the engine to areas of interest and an optical head coupled tothe delivery mechanism distal end. The optical head includes anobjective lens capable of transmitting a foveated image with a firstcentral image portion having a first angular field of view andmagnification that is included within and subtended by a second outerconcentric image portion having a second wider angle field of view andlower magnification. The optical head also includes a first liquid lens,for selectively separately transmitting the first or second imageportions that were received from the objective lens and a second liquidlens for selectively enhancing focus of image portions received from thefirst liquid lens. The respective lenses are coupled in fixed axialpositions along a common optical path within the optical head. Anelectronic image sensor is optically coupled to the second liquid lens,for common capture and transmission of image portions received from thesecond liquid lens. A liquid lens control system is coupled to the firstliquid lens for selectively causing the first liquid lens to transmitsequentially and separately the first and second image portions receivedfrom the objective lens, and coupled to the second liquid lens forselectively causing the second liquid lens to enhance focus of imageportions transmitted by the first liquid lens. An imaging system iscoupled to the common electronic image sensor, generating both first andsecond captured image portions and subsequently displaying themsimultaneously on a common video display viewable outside the exteriorof the inspected turbine engine.

Yet other embodiments of the invention feature a method for dual fieldof view internal visual inspection of a turbine engine by providing aninspection system including a borescope capable of generating a zoommagnification image on a single optical path. The zoom image includes afirst image portion having a first angular field of view andmagnification and a second image portion having a second wider anglefield of view and lower magnification. The borescope is inserted from anexterior of a turbine engine through engine internal passages. Duringinspection, the inspection system captures first and second imageportions separately and sequentially. The system also simultaneouslyseparately displays both of the first and second separately capturedimage portions on a common video display that is coupled to theinspection system. During inspection the borescope is navigated throughengine internal engine passages to one or more predetermined inspectionareas of interest or potential inspection areas of interest areidentified by referencing the displayed second image portions. Areas ofinterest are inspected by referencing the magnified first image portion.

The respective features of the exemplary embodiments of the inventionmay be applied jointly or severally in any combination orsub-combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention can be understood by consideringthe following detailed description in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram of an exemplary embodiment of a turbine engineinternal visual inspection system;

FIG. 2 is a fragmented plan view of an exemplary embodiment of a turbineengine internal visual inspection system being used to perform aninternal inspection of a combustion turbine;

FIG. 3 is a schematic axial elevational view of an exemplary embodimentof an optical lens train and image sensor for a visual inspection systemoptical head;

FIG. 4 is a perspective view of an exemplary embodiment of an opticalhead showing visual inspection of an object of interest; and

FIG. 5 is an image processing flow chart comparing an original object ofinterest, a foveated image captured by an exemplary embodiment of aturbine engine internal visual inspection system of the invention andsimultaneous dual display of the foveated image magnified first imageportion and the wider FOV second image portion.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

Exemplary embodiments described in greater detail herein incorporatezoom or foveated image optical heads that are inserted to combustion orsteam turbine engines internal areas of interest. The foveated imageoptical head has a central first image portion having highermagnification and smaller field of view that is included within andsubtended by a second image portion having a wider field of view andlower magnification. The foveated image first magnified image portionand second wide angle image portion are separately simultaneouslydisplayed on a common display, so that navigation position of theoptical head and the magnified inspection image are correlated. In thisway an inspector can confirm what area of interest within the turbinehas been inspected while evaluating the adjacent magnified inspectionimage. The dual images correlation can be documented, such as by storingthe simultaneously displayed images. In some exemplary embodiments thefoveated image is generated with a monolithic aspheric objective lens.In other exemplary embodiments a first liquid lens is aligned along thesame optical path as the objective lens for selectively transmitting thefoveated image first or second portions. In other exemplary embodimentsa second focusing liquid lens is aligned along the same common opticalpath as objective lens and the first liquid lens for selectivelyfocusing images. The foveated image optical head facilitates maneuveringthe borescope optical head through the turbine engine with the widerfield of view second image portion to areas of interest, then performinga more detailed inspection by viewing the higher magnification firstimage portion. The optical head lenses are in fixed positions, sharing asingle, common optical path and a common electronic image sensor. Thislens and detector arrangement facilitates construction of a compactoptical head, which in some embodiments has an outer diameter of lessthan 11 mm and an axial length less than 40 mm, allowing passage throughsmall diameter engine inspection ports.

FIGS. 1 and 2 show block diagrams of the functional components of anexemplary embodiment of a combustion turbine internal inspection systembeing used to perform inspection of a gas or combustion turbine engine10 vane rows 12 and blade rows 14. The inspection system 20 is alsoutilized for internal inspection of other power plant apparatus, such assteam turbines, heat exchangers, turbo generators or other industrialapparatus. The remainder of this description focuses on application ofthe inspection system 20 embodiments of the present invention tointernal inspection of combustion or gas turbine engines 10; includingengines that are still in cool down phase at temperatures greater than60° C. A gas turbine engine 10 rotating blade row 14 area of is beingvisually inspected internally within the assembled engine by a borescope22, which includes an optical head 24 that is capable of generating andcapturing a foveated image. The foveated image comprises a first centralimage portion having a first angular field of view (FOV1) andmagnification that is included within and subtended by a second imageportion having a second wider angle field of view (FOV2) and lowermagnification. A delivery mechanism 26, such as a flexible conduit,flexible sheath motorized or non-motorized articulated arm or the likeis used to insert, thread or otherwise snake the optical head 24 throughinternal passages of the turbine engine 10, including for examplethrough inspection ports. A control system with coupled visual display28 is communicatively coupled to the optical head 24. The control system28 controls and operates mechanisms within the optical head 24 andgathers images for processing and display. A lighting system 30 providesan illumination source for the optical head 24 to aid in internal visualinspection of the turbine engine.

Referring more specifically to FIG. 2, the control system 28 includes acontroller 32 and coupled human machine interface (HMI)/display 34,exemplary embodiments of all of which can be incorporated within acommercial off-the-shelf tablet computer hardware platform. Thecontroller 32 tablet computer embodiment incorporates a computerprocessor that accesses and executes non-volatile instruction setsstored in the device's own or external memory. While there is referenceto an exemplary control system 28 controller platform architecture andimplementation by software modules executed by the processor, it is alsoto be understood that exemplary embodiments of the invention may beimplemented in various forms of hardware, software, firmware, specialpurpose processors, or a combination thereof. Preferably, aspects of theinvention embodiments are implemented in software as a program tangiblyembodied on a program storage device. The program may be uploaded to,and executed by, a machine comprising any suitable architecture.Preferably, the machine is implemented on a computer platform havinghardware such as one or more central processing units (CPU), a randomaccess memory (RAM), and input/output (I/O) interface(s). The computerplatform also includes an operating system and microinstruction code.The various processes and functions described herein may be either partof the microinstruction code or part of the program (or combinationthereof) which is executed via the operating system. In addition,various other peripheral devices may be connected to thecomputer/controller platform. For example, data and/or image storageand/or auxiliary memory 36 are communicatively coupled to the controller32 directly or by data bus 38, such as an Internet data bus. Inalternative embodiments, the HMI/display 34 comprises a wearabledisplay, such as a wrist-mounted display or eyeglass-type display, forease of inspector mobility. Wearable display and/or HMI control devicesfacilitate hands-free inspection so that the inspector is not requiredto hold a display computer tablet device or be anchored to a fixedposition monitoring station.

FIGS. 3 and 4 show an exemplary embodiment of an optical lens train orsystem for creating a foveated image of an area to be inspected that iswithin the lens train overall field of view (FOV), comprising the firstcentral image portion having the first angular field of view (FOV1) andmagnification that is that is included within and subtended by thesecond outer concentric image portion having the second wider anglefield of view (FOV2) and lower magnification. As can be seen readily bythe light trace paths shown in FIG. 3, the optical head 24 lens trainoptical layout comprises along the same optical path: an objective lensor lens array 40 that provides the foveated image with aspheric, orspherical lenses or combination of both; a magnification/focusing rangelens array 50; and a chromatic and aberration correction lens array 60.Light rays exiting the correction lens array 60 are directed to theimage sensing system 70 that converts the transmitted optical image to aseries of electrical signals for subsequent image processing and displayby the control/display system 28.

In some embodiments the objective lens system 40 comprises a frontelement monolithic aspheric objective lens 42 and image focusingspherical lens 44. The front element 42 aspherical surface is designedto modify the distortion and provide the magnified area (FOV1) at theimage center. Selection of the foveated image first central imageportion (FOV1) or the entire subtending wider image portion (FOV2) isprovided by a first liquid lens 52, which captures and transmits thefull foveated image in response to an actuation voltage V₀ that is sentby the controller 32. In some embodiments the first liquid lens 52 canbe switched to capture and transmit only the central first image portionFOV1 in response to an actuation voltage V₁ that is sent by thecontroller 32. The controller 32 synchronizes the first liquid lens 52switching actuation frequency with the image sensing system 70 samplingrate, so that image capture is coordinated with the desired image fieldof view, FOV1 or FOV2. It is noted that in some embodiments the firstliquid lens 52 is eliminated, in which case only the raw compositefoveated image is transmitted by the objective lens system 40. Additionof the first liquid lens 52 allows selective downstream transmission ofeither the first (FOV1) or second (FOV2) image portions by altering thetransmitted light rays effective focal length where they are redirectedto strike the fixed position image sensing system 70.

In other embodiments that do not include a foveated objective lenssystem 40, simple separate wide angle and magnified images are providedthat are desirably shown simultaneously on a dual display. In suchsystems, the lens system 40 does not include foveated lenses, but ratherconventional image lenses. Magnification adjustment is provided by amagnification first liquid lens 52 that functions as a switch to captureand transmit only a magnified first image portion FOV1 or only the widerangle second image portion FOV2 in response to an actuation voltage V₁or V₂ that is sent by the controller 32. The controller 32 synchronizesthe first liquid lens 52 switching actuation frequency with the imagesensing system 70 sampling rate, so that image capture is coordinatedwith the desired image field of view/magnification.

In some embodiments, such as those of FIGS. 3 and 4 a downstream secondliquid lens 56 is used selectively to enhance focus of the imagetransmitted from the first liquid lens 52. Focus enhancement adjustmentby the second liquid lens 56 is performed manually or automatically bycausing the control system/display 28 controller 32 to alter energizingvoltage ΔV₃ supplied to the focusing liquid lens, synchronized asnecessary with the first liquid lens 52 actuation voltage and theimaging system 70 image sampling rate. In either foveated ornon-foveated image inspection systems, an optical aperture 54 can, butis not required, to be placed between the first and second liquid lenses52, 56 in order to reduce optical aberrations. It is noted that eitherof the liquid lenses 52, 56 alone or in combination can be incorporatedinto the optical head 24, depending upon the desired functionality ofthe inspection system. If an inspection application only requires acomposite foveated image the first liquid lens 52 can be eliminated, asthere is no need to switch between the wide field of view and thecentral image portions of the composite foveated image. Alternatively ifan inspection application does not require fine focusing adjustment ofinspection images the second liquid lens can be eliminated. However,incorporation of both of the liquid lenses 52 and 56 provides morevisual inspection flexibility (e.g., selective central image or widefield image viewing and focusing capability).

In the embodiments shown in FIGS. 3 and 4, a lens stack ofchromatic/aberration corrective lenses 62 are interposed between themagnification/focusing lenses 50 and the image sensing system 70, whichcollectively correct spatial and spectral distortion before reaching theelectronic image sensor 74. While four corrective lenses are shown inthe lens stack 62 in other inspection applications no corrective lensesmay be needed and in other applications one or more lenses may beneeded.

The image sensing system 70 includes a known electronic sensor 74element array of detector pixels, such as a charge coupled device (CCD)that converts light photons striking each pixel to electrical signalsthat is sampled by the controller 32 at a desired sampling rate forsubsequent image processing by the control/display system 28. Aspreviously mentioned the electronic sensor 74 sampling rate issynchronized with the activation frequency of either or both of thefirst or second liquid lenses 52, 56. The prism 72 redirects light raysexiting the correction lens array 60 radially toward the sensor 74. Inthis way a larger sensor array surface area may be packaged within theoptical head 24 envelope than if the sensor had to be positioned axiallydownstream of the correction lens array 60 in alignment with housingradius. Thus the inspection system resolution is also enhanced byincreasing the number of available sensor elements in the electronicimage sensor array 74. A sensor readout board (not shown) is typicallyinterposed between the sensor 74 output and the controller 32.

The borescope optical head 24 component and delivery system packagingare shown in greater detail in FIG. 4. All of the optical lenses 42, 44,52, 56, 62 the optical prism 72 and the electronic image sensor 74 areall optically aligned along a common, shared optical path and are infixed positions relative to each other within the optical head 24. Byelimination of mechanical focusing or image magnification relativemovement between optical components the optical head outer housing tube25 axial length L and diameter D are reduced so that the borescope canbe inserted within turbine engine inspection ports as small as 12 mmdiameter. In exemplary embodiments the optical head 24 maximum diameterD is 11 mm and axial length L does not exceed 40 mm. It is possible toconstruct an optical head having an axial length not exceeding 30 mm.The optical head 24 also optionally includes a fiber optic light pipe 80that is optically coupled to an illumination source within the externallighting system 30. Additionally, rigid position optical lens elementsand detector elements utilized in embodiments herein have less risk ofeither thermal or mechanical distortion/damage than components that moverelative to each other.

In FIG. 4, a resolution test chart is the object of interest 90 beinginspected by the borescope 22 and the turbine visual inspection system20, with the first central part of the foveated image (FOV1) beingenlarged and magnified more than the relatively wider field of viewouter concentric portion FOV2. FIG. 5 shows exemplary image processingof the originally inspected object 90 to the fully captured foveatedimage 92, prior to any post image gathering processing to removedistortions, enhance or alter images gathered by the electronic imagesensor, using known image processing methods. Alternatively the liquidlens 52 can be actuated by the controller to transmit only the centralportion image 96 (FOV1) or only the concentric outer portion image 94(FOV2). It is noted that the entire field of view of the object 90appears in the wide angle image 94 though in smaller magnification thanthe magnified center image 96. Unlike some known “nested” opticalsystems that display “donut” images with missing centers, the presentinvention wide angle image 94 is not missing any of the central portionsof the object of interest 90.

In many inspection applications it is desirable to have both themagnified image 96 and the wide angle image 94 simultaneously availablefor joint inspection on a common viewing display 34, as shown in FIG. 5,whether a foveated objective lens system 40 or a non-foveated objectivelens system is employed within the inspection system. In this wayinspection personnel can readily associate the magnified image 96inspection details with navigational physical location within theinspected object that is afforded by the wide angle image 94. Inexemplary embodiments, simultaneous dual central/wide angle imagedisplays can be viewed on the inspection display screen 34 by causingthe controller 32 to sequentially alternate two of the voltage pairsV₀/V₁ or V₁/V₂ that is applied to the first liquid lens 52, so that forexample the last most recently generated central/wide angle image pairsare shown on the display screen. In the dual display mode the controller32 can also automatically alter the voltage V₃ applied to the focusingsecond liquid lens 56 so that the displayed images are sharply in focus.When simultaneous dual view image display is desired, the controller 32synchronizes the liquid lenses 52, 56 actuation frequencies with theelectronic image sensor array 74 sampling rate. A suggested minimumsynchronization frequency is 10 Hz, so that an inspector viewing thedual images does not perceive excessive display image fluctuation.

An internal visual inspection of a turbine engine is performed asfollows, referring to FIGS. 1 and 2. First, the borescope 22 is insertedinto the turbine engine 10 through engine internal passages, such as aninspection port, by advancing the flexible delivery mechanism conduit 26to an internal area of interest for example visual inspection of turbinevanes 12 and turbine blades 14. Foveated images of the blades 14 arecaptured by the optical head 24 and forwarded to the control/displaysystem 28 where they can be recorded on the data storage device 36and/or transmitted to remote sites via data bus 38. The entire foveatedimage 92 and/or its magnified central first portion 96 (FOV1) and/or itsouter wider field of view second portion 94 (FOV2) can be selectivelydisplayed on the HMI/display 34, depending upon the actuation voltagethat is applied to the liquid lens 52 by the controller 32. In someembodiments the first and second image portions 96, 94 are displayedsimultaneously on a common video display viewing screen image, as shownin FIG. 5. As noted previously, the viewing screen can be incorporatedinto a fixed work station, a portable tablet computing device or awearable device, including eyeglasses. Also as noted previously, usingknown image processing methods the control/display system 28 optionallycan perform post image gathering processing to remove distortions,enhance or alter any of the images gathered by the electronic imagesensor, such as shown in the wide angle image 94.

It is to be understood that, because some of the constituent systemcomponents and methods for performing turbine internal inspectiondescribed herein are preferably implemented in software instruction setsexecuted by the controller 32 (e.g., a tablet computer), the actualconnections between the system components (or the inspection processsteps) may differ depending upon the manner in which the exemplaryembodiments are programmed in the software instruction sets.Specifically, any of the computer platforms or devices may beinterconnected using any existing or later-discovered networkingtechnology and may also all be connected through a lager network system,such as a corporate network, metropolitan network or a global network,such as the Internet.

Although various embodiments that incorporate the invention have beenshown and described in detail herein, others can readily devise manyother varied embodiments that still incorporate the claimed invention.The invention is not limited in its application to the exemplaryembodiment details of construction and the arrangement of components setforth in the description or illustrated in the drawings. The inventionis capable of other embodiments and of being practiced or of beingcarried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass direct and indirect mountings,connections, supports, and couplings. Further, “connected” and “coupled”are not restricted to physical or mechanical or electrical connectionsor couplings.

What is claimed is:
 1. A method for dual field of view internal visualinspection of a turbine engine, comprising: providing an inspectionsystem, including a borescope having: an objective lens system with atrain of fixed-position objective lenses that are aligned on a singleoptical path, for refracting an incident image into a single, refracted,foveated output image including a first central output image portionhaving a first angular field of view and magnification that is includedwithin and subtended by a second output image portion having a secondwider angle field of view and lower magnification, a first liquid lensdownstream of and optically aligned along the single optical path of theobjective lenses, for selectively separately transmitting the first orthe second image portions of said refracted, foveated output image, anda single electronic, sensor element array of detector pixels downstreamof the first liquid lens and optically aligned along the single opticalpath of the objective lenses and the first liquid lens, for capturingall of said single, refracted, composite, foveated output image thereupon in a single sample; inserting the borescope from an exterior of aturbine engine through engine internal passages to an internal area ofinterest; transmitting with the first liquid lens and capturing on thesingle electronic, sensor element array the first image portion of theinternal area of interest within the engine with the inspection system;separately transmitting with the first liquid lens and capturing on thesingle electronic, sensor element array the second image portion of theinternal area of interest within the engine with the inspection system;and simultaneously separately displaying both of the first and secondseparately captured image portions on a common video display that iscoupled to the inspection system.
 2. The method of claim 1, the providedborescope further comprising a monolithic aspheric objective lens in theobjective lens system for refracting said refracted, foveated outputimage and a first liquid lens for selectively separately transmittingthe first or second image portions of said refracted, foveated outputimage that were received from the monolithic aspheric objective lens. 3.The method of claim 2, the provided borescope further comprising asecond liquid lens for selectively enhancing focus of the refracted,foveated output images received from the first liquid lens, with all ofthe respective lenses coupled in fixed axial positions along a shared,single optical path with said electronic sensor element array within anoptical head.
 4. A method for dual field of view internal visualinspection of a turbine engine, comprising: providing an inspectionsystem including: a borescope having: an elongated delivery mechanismhaving a distal end for insertion from an exterior of a turbine enginethrough internal passages within the engine to areas of interest; anoptical head coupled to the delivery mechanism distal end, sharing on acommon, single optical path: an objective lens system with a train offixed-position objective lenses, for refracting an incident image into asingle, refracted, foveated output image including a first central imageportion having a first angular field of view and magnification that isthat is included within and subtended by a second outer image portionhaving a second wider angle field of view and lower magnification, afirst liquid lens, for selectively transmitting said refracted, foveatedoutput image first or second portions that were received from theobjective lens system, a second liquid lens for selectively enhancingfocus of the refracted, foveated output image first or second portionsreceived from the first liquid lens, with the respective objective,first liquid, and second liquid lenses coupled in fixed axial positionsalong the shared single optical path within the optical head, a singleelectronic image sensor element array of detector pixels opticallycoupled to the second liquid lens, for common sample, capture andtransmission of all portions of all refracted, foveated images receivedfrom the second liquid lens, a liquid lens control system coupled to thefirst liquid lens, for selectively causing the first liquid lens totransmit first or second portions of said refracted, foveated imagesreceived from the objective lens, and coupled to the second liquid lensfor selectively or automatically causing the second liquid lens toenhance focus of the images transmitted by the first liquid lens, and animaging system coupled to the common said electronic image sensorelement array, for selectively generating said foveated image firstand/or second portions, viewable outside an exterior of the inspectedturbine engine; inserting the inspection optical head from an exteriorof a turbine engine to an internal area of interest within by routingthe delivery mechanism through engine internal passages; causing thefirst liquid lens to transmit sequentially separate first and secondimage portions of the internal area of interest within the engine withthe liquid lens control system; separately capturing the first andsecond image portions of said refracted, foveated image transmitted bythe first liquid lens with the electronic image sensor, for furtherprocessing by the imaging system; and simultaneously separatelydisplaying both of the first and second separately captured imageportions on a common video display that is coupled to the imagingsystem.
 5. The method of claim 4, the liquid lens control systemautomatically controlling the first and second liquid lenses to focusimages transmitted by the first liquid lens.
 6. The method of claim 5,the provided borescope optical head further comprising at least onecorrective lens oriented in the common optical path between the secondliquid lens and said electronic image sensor element array for imagechromatic and/or aberration correction.
 7. The method of claim 4, theprovided borescope optical head further comprising at least onecorrective lens oriented in the common optical path between the secondliquid lens and said electronic image sensor element array for imagechromatic and/or aberration correction.
 8. The method of claim 4, theprovided inspection system further comprising a monolithic asphericobjective lens; and a hands-free, human wearable common video display.9. A turbine engine dual field of view internal inspection system,comprising: a borescope having: an elongated delivery mechanism having adistal end for insertion from an exterior of a turbine engine throughinternal passages within the engine to areas of interest; an opticalhead coupled to the delivery mechanism distal end, sharing on a single,common optical path: an objective lens system with a train offixed-position objective lenses, for refracting an incident image into asingle, refracted, foveated output image including a first central imageportion having a first angular field of view and magnification that isthat is included within and subtended by a second outer image portionhaving a second wider angle field of view and lower magnification, afirst liquid lens, for selectively transmitting said refracted, foveatedoutput image first or second portions that were received from theobjective lens system, a second liquid lens for selectively enhancingfocus of the refracted, foveated output image first or second portionsreceived from the first liquid lens, with the respective objective,first liquid, and second liquid lenses coupled in fixed axial positionsalong the shared, single optical path within the optical head, a singleelectronic image sensor element array of detector pixels opticallycoupled to the second liquid lens, for common sample, capture andtransmission of all portions of all refracted, foveated images receivedfrom the second liquid lens, a liquid lens control system coupled to thefirst liquid lens for selectively causing the first liquid lens totransmit first or second portions of said refracted, foveated imagesreceived from the objective lens, and coupled to the second liquid lensfor selectively or automatically causing the second liquid lens toenhance focus of the images transmitted by the first liquid lens, and animaging system coupled to the common said electronic image sensorelement array, generating both first and second separately capturedimage portions and subsequently displaying them simultaneously on acommon video display viewable outside the exterior of the inspectedturbine engine.
 10. The system of claim 9, the objective lens systemfurther comprising a monolithic aspheric objective lens.
 11. The systemof claim 9, the borescope optical head further comprising at least onecorrective lens oriented in the common optical path between the secondliquid lens and said electronic image sensor element array, for imagechromatic and/or aberration correction.
 12. The system of claim 9, theliquid lens control system automatically controlling the first andsecond liquid lenses to focus images transmitted by the first liquidlens.
 13. The system of claim 12, the liquid lens control systemapplying a first voltage level to the first liquid lens for transmittingthe first image portion and applying a different second voltage levelfor transmitting the second image portion at a modulation frequency thatis synchronized with sampling rate of said electronic image sensorelement array.
 14. The system of claim 13, the liquid lens controlsystem applying sequentially the first and second voltage levels to thefirst liquid lens at the modulation frequency and the imaging systemthen sequentially displaying most recent pairs of first and second imageportions that were sampled by said electronic image sensor elementarray.
 15. The system of claim 9, the liquid lens control systemapplying a first voltage level to the first liquid lens for transmittingthe first image portion and applying a different second voltage levelfor transmitting the second image portion at a modulation frequency thatis synchronized with sampling rate of said electronic image sensorelement array.
 16. The system of claim 15, the liquid lens controlsystem applying sequentially the first and second voltage levels to thefirst liquid lens at the modulation frequency and the imaging systemthen sequentially displaying most recent pairs of first and second imageportions that were sampled by said electronic image sensor elementarray.
 17. The system of claim 9, further comprising an illuminationsource coupled to the optical head.
 18. The system of claim 9, theborescope optical head further comprising an optical prism oriented inthe common optical path between the second liquid lens and saidelectronic image sensor element array; and an optical head maximumdiameter of 11 millimeters.
 19. The system of claim 9, the imagingsystem compensating for image distortion in images captured by saidelectronic image sensor element array.
 20. The system of claim 9,further comprising an image recording system.
 21. A method for dualfield of view internal visual inspection of a turbine engine,comprising: providing an inspection system, including a borescope withan objective lens system having a train of fixed-position objectivelenses, which train of lenses includes a zoom magnification, monolithicaspheric objective lens, which are all aliened on a single optical path,for refracting an incident image into a single, refracted, foveatedoutput image including a first central image portion having a firstangular field of view and magnification and that is included within andsubtended by a second image portion having a second wider angle field ofview and lower magnification, and single electronic, sensor elementarray of detector pixels downstream of and optically aligned along thesingle optical path of the objective lense train, for capturing all ofsaid single, refracted, foveated output image there upon in a singlesample; inserting the borescope from an exterior of a turbine enginethrough engine internal passages; capturing separately and sequentially,with a first liquid lens that is downstream of the zoom magnification,monolithic aspheric objective lens, first and second image portions withthe inspection system on said electronic sensor element array along saidsingle optical path; simultaneously separately displaying both of thefirst and second separately captured image portions on a common videodisplay that is coupled to the inspection system; navigating theborescope through engine internal engine passages to one or morepredetermined inspection areas of interest or identifying potentialinspection areas of interest by referencing the displayed second imageportions; and inspecting the areas of interest by referencing themagnified first image portion.